Among the many alien powers of the galaxy in Star Trek and The Next Generation, are some comparatively minor races, although only occupying a small area of space, can a pose a military challenge to one of the major powers.
The Tholians are a race of beings that evolved in a searing hot methane environment, and seem to possess a hive culture similar to the Borg. However, although Tholians are modified to perform specific functions from birth, they are more individualistic than the Borg, operating in a similar manner to other life forms, but with some of the traits of the Hive Culture. These traits lead them to function slightly more efficiently than other races, but they are not as single minded at the Borg.
The Tholians are fiercely isolationist, guarding their borders against any intrusion, with constant patrols. It is not known if the Tholians are simply not interested in expansion, or biding their time in order to wait for the right moment. At present, they're not interested in forming trade links with any other space-faring culture.
The Tholian Navy
The Military Arm (it is not known if there is a civilian population) of the Tholian Assembly, when first encountered by the Federation, seemed based entirely on defensive tactics and design theories. The major weapon of the time was an energy web. Two or more Tholian craft would weave their energy web around a starship, then tow it back to a base. This worked fine on Federation vessels which strayed into Tholian space. However, when a Klingon K'agga Class Cruiser was approached in this manner, the Captain was unwilling to simply sit in space and allow this to happen.
After the four Tholian craft were destroyed, and the Klingon vessel went on its way, the Tholian military went through a drastic rethink. For nearly a year, there was very little contact between the Tholians and any outside cultures. Then they came back.
The old style Tholian vessels had undergone a drastic re-fit, with the actual Web Generators reduced to a secondary system. An entire new range of combat vessels were deployed, all with a vastly improved offensive capacity. It is thought of as poetic justice that the first vessel to experience the business end of the new Tholians was a Klingon K't'inga Class Cruiser. In a fierce confrontation, the Klingon vessel barely managed to limp away, whereas the Tholian ship was practically undamaged. The lesson was well learnt, and the Tholian ships were never underestimated again.
Guardian Class Patrol Cruiser
Defender Class Light Cruiser
Balwark Class Medium Cruiser
Bastion Class Heavy Cruiser
Repulse Class Battlecrusier
Retribution Class Battleship
This is an extension of the Web Generator technology. A small portion of web is produced in a special firing chamber, then projected at the target. It envelopes the enemy vessel, then constricts, burning up its energy as it shrinks. Eventually, there is insufficient energy remaining in the web for it to remain cohesive, and it "falls apart". However, any target hit by such a weapon may not fire torpedoes of any kind in the turn, as they will strike the web and explode.
The Web Crusher cannot cause critical hits, as the damage is spread too widely about the target. To-hit numbers improve with the size of the weapon, as the actual web generated is larger. The damage is scored by rolling the appropriate dice, applying the modifiers as given, and reducing the damage by one per functioning screen.
Well that's it for the Tholians. I find the concept fascinating, and it is a shame that the Next Generation did not choose to expand on this race, although they have been mentioned on at least two occasions, are important enough to be included in Starfleet Combat Simulations (see Data's analysis of Commander Riker's command ability in the Season Two episode "Peak Performance").
Also, in Classic Trek (or TOS), they were one of the only minor races to get their own starship model (even the Klingons had to wait for Season Two), although they did glue a couple of Warp nacelles on it, and use it in the infamous "Revenge of the Space Hippies" episode!
The Tholians have now made an appearance in Enterprise the new series of Star Trek based before TOS.